1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having a semiconductor body which at a surface is provided with circuit elements and a multilayer wiring structure, in which the surface of the semiconductor body is coated with a first layer of insulating material on which there is formed from a metal layer deposited on the insulating material a first conductor pattern which contacts the semiconductor body at the area of contact holes in the first layer of insulating material and comprises at least one plate of a capacitor, after which a second conductor pattern is applied, which comprises a second plate of the capacitor and is separated therefrom by a dielectric obtained by anodic oxidation from the metal layer deposited on the first layer of insulating material.
The invention also relates to the device obtained by this method.
2. Description of the Prior Art
For the manufacture of capacitors in semiconductor devices for electronic applications, the thin-film technique is preferably used, the capacitors manufactured according to this technique having a larger capacity per unit surface area and having considerably lower parasitic resistances than the capacities of the diffused junctions that can also be used. Further the capacity of the thin-film capacitors is not dependent upon the applied voltage, as such is the case with the semiconductor junctions.
The insulating material used in these capacitors as a dielectric is mostly silicon oxide (SiO.sub.2), because this oxide is formed during most of the methods for manufacturing devices from silicon substrates. However, this oxide has a low permittivity.
Since it is difficult to obtain this oxide in a very small thickness due to the risk of the occurrence of defects in the insulation, endeavors have been made to replace this dielectric by other materials of higher permittivity, especially by silicon nitride, both alone and together with silicon oxide, and more recently by aluminum oxide or aluminum oxide together with a layer of the said silicon oxide.
The known methods of obtaining homogenous and dense thin layers of these dielectrics generally require additional often complicated or very accurate treatments which require expensive measures to be taken. This is the case as to the layers of silicon oxide or of silicon nitride. This is the reason why there is generally an increasing tendency to use anodic oxidation for forming an oxide layer from the surface of an already deposited metal layer, a suitable voltage then being applied between the said metal surface to be oxidized and an electrode immersed in an electrolyte.
This solution is of special importance when the manufacture of so-called "MOM" (Metal--Oxide--Metal) capacitors is concerned because the dielectric layer of the capacitor can be formed in the first deposited metal layer.
Such a method is known from the French Patent Specification No. 2,138,339.
A choice can then be made not only with respect to the nature of the metals used, but also with respect to the composition of the electrolyte used for the anodization. It appears that during anodization of an aluminum layer given solutions used as the electrolyte, which, for example, contain oxalic acid and glycol ethylene, lead to a porous aluminum oxide layer. This phenomenon is often very unfavorable because aluminum is one of the metals which are most frequently used for the manufacture of contacts in semiconductor devices for electronic applications (transistors or integrated circuits) and for the manufacture of integrated capacitors; in these circumstances, the aluminum can diffuse into the porous aluminum oxide, which involves the risk of short circuits.
In order to mitigate this disadvantage, a protective layer is often applied consisting of a metal which prevents this diffusion, for example, nickel, which is deposited on either side of an aluminum oxide layer, but this method, which then comprises additional steps, thus becomes more complicated and more expensive.
On the other hand, it is known that, taking into account the density of the active or passive elements to be manufactured in an electronic microcircuit, the electrical connections between the various elements require an extensive network of contacts and interconnections, which for reasons of accomodation can be provided only in the form of juxtaposed layers separated by insulating layers (multilayer structure).